Alexei Navalny back on Russian presidential campaign trail after 20-day jail term for protests against Vladimir Putin

Moscow: Russian opposition leader Alexei Navalny walked free on Sunday after a 20-day jail term for organising protests against President Vladimir Putin.

Navalny, who has declared his intention to stand for president in 2018, was released in a secret location in Moscow early Sunday to evade media attention.

"Hi. I'm out," Navalny wrote on Instagram, posting a picture of himself on a street. A photographer working for his team later posted photographs of him meeting colleagues at the office of his anti-corruption foundation.

Russian opposition leader Alexei Navalny after his release from jail in Moscow. AP

During Navalny's time behind bars, the Kremlin race he hopes to contest has heated up with television star Ksenia Sobchak throwing in her hat.

Navalny posted he was "ready to work" and later met supporters at a rally in the southern city of Astrakhan — around 1,300 kilometres southeast of Moscow — which was allowed to go ahead by the authorities.

He told the 300 who gathered in the rain: "Do we need this kind of power that makes fun of us? No, and that's why I'm a candidate, the right candidate for Astrakhan."

Navalny wrote jokingly that while in jail he had read 20 books, learnt a few words of the Kyrgyz language and drunk 80 litres (20 gallons) of tea.

Earlier Sunday, supporters of Navalny hung a banner from a bridge close to the Kremlin reading: "It's time to get rid of Putin and time to elect Navalny."

The charismatic 41-year-old lawyer informally launched a presidential bid in December last year and has since opened campaign offices and held rallies countrywide to consolidate supporters.

Earlier this year he served sentences of 15 days and 25 days for organising unauthorised anti-Putin protests.

During his latest jail term, his supporters held rallies on Putin's birthday on 7 October, with more than 270 detained nationwide.

He has faced a constant stream of official bans on public meetings, as well violent attacks on him and his supporters and vandalism of his offices.

During Navalny's latest period in isolation in a Moscow detention centre, another high-profile figure has joined the presidential race.

Sobchak, a socialite and television star and the daughter of President Vladimir Putin's late mentor, launched her bid to stand on Wednesday.

The presidential race has yet to officially begin and Putin has not yet declared his participation in the March 2018 election. However he is widely expected to seek and win a six-year term that would extend his rule till 2024.

Sobchak has vowed to back Navalny's bid to be included in the race — as electoral authorities say his suspended sentence for fraud makes him ineligible to stand until 2028.

However, many liberals see her as a Kremlin-backed spoiler candidate brought in to give the race a veneer of opposition.

Putin worked closely with her late father Anatoly Sobchak when he was a liberal St Petersburg mayor, and has acknowledged his importance as a mentor.

Navalny has yet to comment on Sobchak's bid, but earlier condemned rumours of her possible candidacy, saying this was a "rather disgusting Kremlin game" and calling her a "liberal laughing stock."

Sobchak, 35, calls herself "the candidate against all".

Russian media focused on her past as host of a reality show called Dom-2, or House-2, where contestants have to form couples, as well as of modelling show Russia's Next Top Model.

"She's going to work according to her profession at the elections: in order to turn non-contested presidential pseudo-polls into the biggest show of 2018," wrote Vedomosti business daily in a Friday editorial.

Navalny sometimes shared a podium with Sobchak at mass rallies against Putin in 2011 and 2012. While he wowed crowds with punchy oratory, Sobchak faced a hostile audience who doubted her sudden backing of opposition causes.

She paid a price for her opposition campaigning, however, losing lucrative television work, and now hosts a show on independent TV Dozhd, or Rain.

Forbes' Russian edition estimates her net worth at $2.1 million.

Sobchak is set to present her campaign to journalists in Moscow on Tuesday.